Modification of Micor Low-Band
Receiverfor use in the 6 meter Ham
Band

By Kevin K. Custer W3KKCwith additions by Sam Kirby, WB4HAP

Concept:
To modify a Motorola Micor Low Band 42-50 Mc. split receiver for use on the 6 meter amateur band.

Modification Description:
This modification involves altering component values in the front-end
and crystal oscillator injection circuitry. This modification will
provide original sensitivity. There are two conversion methods listed here. Both will work
satisfactorily.
The second "better" conversion came directly from the Motorola engineering department in the
late 70s’ by hams that worked there. Doing the second modification will
produce a board that will meet or exceed design parameters for each individual
circuit. (The values, after all, were determined by the origional Motorola engineers!)
Some of these cap values are hard to find. They can possibly be found in
other boards of different ranges. (Sometimes it good to have a pile of junk boards laying
around.)

Important Note:
Be certain the receiver operates correctly on the origional frequency range before attempting
to modify it for the new band. You may want to document the sensitivity
of your particular unit, using your test equipment, so you know what to
expect after the conversion is done. Please read through these instructions completely
to become familiar with each procedure before attempting the conversion.

Micor Receiver Modification - Simple Method
Capacitor Replacement: Remove the aluminum shields from coils
to gain access to the capacitors.
Remove and replace the following capacitors with the values indicated.
Replacement capacitors should be of the same type and style as the
original.

Micor Receiver Modification - Better Method
From the Motorola Engineering Labs Component Replacement:
Remove the aluminum shields from coils to gain access to the components.
Remove and replace the following components with the values indicated.
Replacement capacitors should be of the same type and style as the
original.

You should be able to obtain original sensitivity on the new band.
The most important adjustment is the discriminator center. If you
have no way of properly checking on the discriminator adjustment, don't
touch it.